Various coatings are known which can be applied to electric lamps for different purposes. For example, light diffusion coatings are used to hide the incandescent filament of an incandescent lamp and which are often applied as a fired enamel or as an electrostatic deposit of colloidal powders. Other colored enamels and electrostatic coatings have been used for quite some time to produce either clear or opaque light transmission of a different color than the emission color of the light source in the electric lamp.
One light diffusing coating of this type is described in U.S. Pat. No. 4,081,709, issued to the assignee of the present invention, which pertains to an electrostatic coating of silica on the inner bulb wall of an electric lamp and which is obtained by controlling the particle size and electrical resistivity of the silica powder. The light diffusion produced in this manner completely hides the lamp filament or other internal lamp structure with little light loss and the aforementioned physical characteristics of the silica powder permit electrostatic deposition to be carried out reliably under varying environmental conditions.
In still pending application Ser. No. 239,595, filed Mar. 2, 1981, in the names of C. B. Collins and W. G. James, and also assigned to the present assignee, there is disclosed an electrostatically deposited coating which produces colored emission from an incandescent lamp through selective light absorption by a particulate opaque colorant in the powder mixture used. This selective light absorption provides effective filtering means whereby the balance of visible radiation produced by the light source is emitted from the lamp with little light loss. The desired effect is produced with a powder mixture utilizing light refractive particles, a selective light absorption particulate colorant, and flux calcined diatomaceous silica with said powder mixture also having a particular particle size range and electrical conductivity characteristic for electrostatic deposition. Useful light refractive particles in said powder mixture can be selected from the group consisting of alumina, silica, aluminosilica, calcium carbonate, and mixtures thereof. A uniform yellow color lamp emission can be obtained with said coating which absorbs blue color radiation in the 390-500 nanometer wavelength region by reason of the absorption characteristics of the particulate colorant material being used.
In the co-pending application Ser. No. 276,975, filed June 24, 1981, now U.S. Pat. No. 4,359,536, also assigned to the present assignee, there is described a frit glass composition which is particularly useful to color the soda-lime glass envelope of incandescent lamps. Specifically, the disclosed glass frit comprises a zinc borosilicate glass composition containing various colored oxides to produce a colored coating when fired on the surface of the lamp glass envelope. Said glass frit has a composition expressed in terms of weight percent, based on the starting batch formulation, as follows: 25-30 ZnO, 12-18 SiO.sub.2, 24-35 B.sub.2 O.sub.3, 1-3 Al.sub.2 O.sub.3, 5-10 Na.sub.2 O, 7-8 CaO, 2-5 BaO, 0.5-3 ZrO.sub.2, 1-2 F, and 0-6 K.sub.2 O except for incidental impurities and refining agents. Typical proportions of inorganic pigment used to produce transparent colored light emission from the coated lamps is said to reside in the range 0.3 to 2.0 weight percent of the total composition.
It would be a desirable to selectively absorb some of the green and yellow radiation emitted from electric lamps while still transmitting the remaining visible light. A pleasant aesthetic result is thereby produced wherein skin tones and other objects being illuminated by the lamp radiation appear more pink in color. Thus, visible radiation from an uncoated incandescent lamp can be improved since the yellow color light causes some skin tones to take on a sallow appearance. It would be further desirable to achieve said objective by means not requiring that the lamp glass envelope itself be modified, however, in order to minimize the cost and impact upon lamp manufacture.